Deputy Senate Sergeant at Arms Martina Bradford said the hackers' attempts to penetrate the Senate network failed. They were able to download some information from the public site, she said, but could not access sensitive data because they were blocked by a firewall.

Over the weekend, a portion of the Senate website was hacked in what Bradford described as a similar attack. Lulz - which is best known for a recent attack on Sony - claimed credit for that attack. The attack prompted a review of Senate web security.

Bradford said Senate networks have been targeted by hackers since they first went online.